1. Field of the Invention
The present invention relates to a mobile communications system, a mobile station, a control method and a recording medium and, more particularly, to a mobile communications system for code division multiple access, comprising a mobile station and base stations.
2. Description of the Prior Art
In the conventional mobile communications system, Location Areas (LAs) are preset. When the location of a User Equipment (UE) that is a mobile station is registered, the location registration information indicating the LA where the UE resides is recorded in a database system called a Home Memory (HM) station. The UE registers the location upon moving from one LA to another LA, and the location registration information in the HM station is updated, whereby no matter where the UE is moved, the location of the UE can be retrieved at any time according to the HM station.
Accordingly, when controlling an incoming call to the UE, referring to the location registration information of the UE that is written in the HM station, incoming call signals are transmitted from all the Base Transceiver Stations (BTSs) within the LA in which the UE exists.
In the conventional mobile communications system, the UE judges the zone (cell) in which the UE exists by measuring a reception level of a control signal received from the BTS forming this zone. FIG. 8 is a diagram for explaining a method for judging the zone. In FIG. 8, the UE measures a electric field strength of the control signal received from the BTS constituting the cell in which the UE exists at present. The UE does not perform a zone transfer processing, if the measured electric field strength is maintained above a threshold value (Pth[dB]) for a predetermined time period (Tselection [sec]). However, the UE performs the zone transfer processing, if the measured electric field strength falls below the threshold value by a predetermined number of times for the time period of Tselection. The zone transfer processing is a cell switching processing, and contains a location registration processing.
If the UE is located in the boundary between LAs, and field strengths of received control signals around the boundary are intermingled, the UE repeats the location registration consecutively. Therefore, a traffic in the location registration is increased.